Wheeled transport is used in a wide variety of functions and pastimes. However, in some circumstances wheels do not work as well as desired. Wheeled transport is not an effective way of moving loads on uneven, loose or soft ground. In particular, problems can arise where movement across an uneven surface is required.
Off-road vehicles are designed for driving on ground that is uneven and which can be muddy. They include several features that make them suitable for this, such as four wheel drive. However, off-road vehicles are still liable to become stuck if they hit an obstacle, such as a rock, a tree trunk or a rut in the terrain.
Endless tracks arranged around fixed wheels are a well-known way of facilitating off-road movement of, for example, military vehicles. However, these do not provide as much movement as may be desirable for certain types of off-road use of a vehicle.
GB 621,584 discloses a load carrying vehicle in which movement is facilitated by endless tracks arranged around a series of sprocket wheels. The load carrying vehicle can be used in a position where the endless tracks are in contact with the ground. In such a position, a hand wheel can be used to rotate the sprocket wheels, thereby moving the vehicle on the endless tracks. This type of vehicle requires the user manually to rotate sprockets engaging the caterpillar track and thus to move the caterpillar track in order to enable the vehicle to move.
U.S. Pat. No. 2,173,793 discloses an endless track vehicle with auxiliary wheels. In this vehicle, the wheels are raised when it is operated with the endless tracks. When not in use (i.e. when travelling on wheels), the endless tracks are raised to increase clearance from the ground.
Thus, in this vehicle, it is not intended that the endless track should come into contact with the ground when the wheels are in use.
EP 0 414 325 discloses a vehicle suitable for on- and off-road use. The vehicle is provided with a frame that supports guiding wheels around which an endless track is arranged. The frame can be lowered when the vehicle is used off-road in order that the track may be driven around the guiding wheels in order to provide traction with the ground. Again, when the frame (and hence the track) is in its raised position, it is not intended that the track should come into contact with the ground. Moreover, were it to come into contact with the ground in its raised position, it would not provide adequate protection to the underside of the vehicle.
DE 36 38 150 describes a drilling trailer with retractable tracks for off road operation. The trailer includes two track units, each comprising a track that can be lowered to contact the ground. The track units are intended to extend hydraulically into an operational position when required for off-road use. Again, these tracks are not intended to contact the ground when in their raised position.
DE 27 53 706 describes an all-terrain vehicle having a retractable track drive. Again, the retractable tracks are intended to be lowered when the vehicle is on an appropriate terrain.
FR 2 677 600 discloses a child's pushchair having a track that lowers to the same level as the wheels when an obstacle is encountered. The track does not facilitate movement when in its raised position, and does not provide any protection to the underside of the pushchair.
The underside of a motor vehicle is generally protected by a sheet of steel. This only offers partial protection to the vehicle since impacts are unable to glance off. Such impacts impede movement (even stopping a vehicle moving altogether) and are liable to damage a vehicle. There is therefore a need for a way of facilitating movement of off-road vehicles across such obstacles, and for providing improved protection to the vehicle.
Wheeled trolleys are often used to enable heavy loads to be moved. However, these can be difficult to use if the surface is anything other than smooth and firm. An improved trolley having the ability to traverse uneven surfaces is needed.
Skiing and sledging are popular winter pastimes, but they require a certain amount of snow fall. It is often not possible to continue with these pastimes in countries having little snow fall, unless specially constructed dry ski slopes are visited. Moreover, it is not possible to pursue these activities in the summer in most places. A means of skiing or sledging on a snow-free surface is desirable.